1. Field of the Invention
The present invention relates generally to a vehicle driving power controller which controls power output of a vehicle so that acceleration of the vehicle approaches the acceleration requested by a driver.
2. Description of the Related Art
Generally, a vehicle equipped with an engine and wheels is required to operate under a variety of running conditions (e.g., various road surface and weather conditions) including those imposed on the vehicle by the driver. The quickness and smoothness of the vehicle's response to changing control input is highly desired. Conventional technology controls vehicular driving power based on the magnitude or stroke of urged accelerator pedal manipulated in part by the driver.
Japanese Unexamined Patent Publication No. 1-294925 discloses a driving power controller which estimates a target acceleration based upon the magnitude of the urged accelerator pedal (i.e., accelerator opening angle) manipulated by the driver. The controller computes a difference or deviation between the estimated target acceleration and actual acceleration. The controller also adjusts an opening degree (i.e., degree of angle) of an engine throttle valve by reference to a data map correlating the computed deviation and estimated target acceleration. Therefore, the actual vehicle acceleration is controlled to approach the target acceleration.
However, any uniform estimate for a target acceleration is set in the data map using only the correlation between the accelerator angle and vehicle speed. Thus, any particular preset target acceleration referenced in the data map may not always match the acceleration or driving power desired by an individual driver according to his or her own driving habit, be it slow, fast or any combination of the two.
Japanese Unexamined Patent Publication No. 4-314940 discloses a technology which solves the above-described drawbacks, improves efficiency of memory usage in the controller and speeds up the computation of target acceleration. According to this technology, an opening angle of a linkless type throttle valve is controlled according to the magnitude of the urged accelerator pedal (i.e., accelerator stroke) manipulated by the driver. A backup RAM in the controller stores data in two dimensional map style for determining the target acceleration in response to the accelerator stroke. Accordingly, the controller controls the opening angle of the throttle valve so that the actual vehicular acceleration approaches the target acceleration determined by reference to the data map, thereby controlling the vehicle driving power.
With conventional technology, the change in the accelerator stroke relative to the actual vehicular acceleration is presumed by the controller to be requested by the driver from sensed changes in the degree of acceleration. The controller corrects data to be stored in the data map so as to minimize the deviation between the requested acceleration by the driver and the target acceleration determined through the data map. The controller re-stores the corrected data in a backup RAM. Data in the data map is revised by correcting the target acceleration relative to the above-described deviation. In other words, the controller receives target acceleration data in response to changes in the accelerator stroke. Since target acceleration data is automatically updated to account for the changes in the magnitude of acceleration required by the driver, the controller calculates a target acceleration corresponding to a particular driver's needs or characteristics.
However, even in this conventional technology, target acceleration data is only corrected or modified and old map data is simply replaced with corrected data to update the target acceleration data. That is, when target acceleration data is to be updated in the data map, it is done so only within the confines of a certain narrow accelerator stroke range for a particular time. For example, when the vehicle is cruising at a constant speed, the controller updates only the target acceleration data corresponding to the accelerator stroke which currently fits the constant cruising speed. Likewise, when the vehicle undergoes sudden acceleration, the target acceleration data is updated by the controller only according to the specific region of the accelerator's stroke range.
According to the above-described manner by which data is updated in the data map, only that portion of the target data corresponding to the limited accelerator stroke region is correctly updated. This results in only a partially updated data map with part of the map containing updated data and part containing old data. Put differently, even if the certain regions of the data map contain updated target acceleration data, because those regions are updated only with respect to a specific accelerator stroke range, other regions of the data map contain target data that remains outdated or uncorrected. Consequently, discontinuities in target acceleration data may form in the data map with respect to a particular range of the accelerator's stroke. Unfortunately, when vehicular drive power is controlled by means of a data map having such discontinuous data, the vehicle is often unresponsive, or at least, insufficiently responsive to the changing acceleration needs of the driver and specifically to the changes in the stroke of the accelerator.